Maintaining cardiovascular health relies on a number of physiological and behavioral mechanisms that monitor, respond to, and alleviate perturbations in body fluid homeostasis. Angiotensin II (AngII), the bioactive product of the renin-angiotensin system, is an important component of these actions, especially in the response to hypovolemia. AngII affects numerous systems including the kidney, adrenal gland, gastrointestinal tract, vascular smooth muscle, and brain. The central effects of AngII include increases in water and NaCl intake, critical behaviors for the maintenance of body fluid and cardiovascular homeostasis. These behavioral effects are mediated largely through AngII type 1 (AT1) receptors, which stimulate several intracellular signaling pathways including one that leads to increased inositol trisphosphate (IP3) formation and protein kinase C (PKC) activation, and another that increases phosphorylation of mitogen activated protein (MAP) kinase. Recent experiments suggest different relative contributions of these pathways to the water and NaCl intake induced by AngII. The experiments in the present proposal use behavioral, pharmacological, electrophysiological, molecular, and neuroanatomical approaches to explore the role of these intracellular signaling pathways in the control of AngII- induced water and NaCl. Specifically, the experiments will (1) determine the roles of the Gq/IP3/PKC and MAP kinase signaling pathways in AngII-induced water and NaCl intake; (2) determine the role of individual signaling pathways on neural activity at primary and downstream sites of AngII action in the brain; and (3) test the role of these signaling pathways and receptor phosphorylation on desensitization of the intracellular and behavioral responses after multiple treatments with AngII. These experiments use a multifaceted approach and a variety of techniques to answer these questions from behavioral, anatomical, electrophysiological, and neurochemical perspectives.